This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPP third generation partnership project
ACK acknowledge
CC component carrier
CCE control channel element
CM cubic metric
DL downlink (eNB towards UE)
DTX discontinuous transmission
eNB EUTRAN Node B (evolved Node B)
FDD frequency division duplexing
EUTRAN evolved UTRAN (LTE, sometimes termed 3.9G)
CQI channel quality indicator
FDD frequency division duplex
FDMA frequency division multiple access
FDPS frequency domain packet scheduler
HARQ hybrid automatic repeat request
HO handover
LB long block
LTE long term evolution
NAK/NACK not acknowledge or negative acknowledge
Node B base station
PRB physical resource block
PDCCH physical downlink control channel
PDSCH physical downlink shared channel
PUCCH physical uplink control channel
RS reference signal
SC-FDMA single carrier, frequency division multiple access
SU-MIMO single user multiple-input multiple-output
TDD time division duplex
UE user equipment
UL uplink (UE towards eNB)
UTRAN universal terrestrial radio access network
A communication system known as evolved UTRAN (EUTRAN, also referred to as UTRAN-LTE or as E-UTRA) is currently under development within the 3GPP. As presently specified the DL access technique will be orthogonal frequency division multiple access (OFDMA), and the UL access technique will be SC-FDMA.
One specification of interest is 3GPP TS 36.300, V8.6.0 (2008 September), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Access Network (E-UTRAN); Overall description; Stage 2 (Release 8), incorporated by reference herein in its entirety.
FIG. 1 reproduces FIG. 4.1 of 3GPP TS 36.300, and shows the overall architecture of the E-UTRAN system. The EUTRAN system includes eNBs, providing the EUTRA user plane (packet data convergence protocol PDCP/radio link control RLC/medium access control MAC/physical PHY) and control plane (radio resource control RRC) protocol terminations towards the user equipment UE. The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an S1 interface to an evolved packet core (EPC), more specifically to a MME (Mobility Management Entity) by means of a S1 MME interface and to a Serving Gateway (S-GW) by means of a S1 interface. The S1 interface supports a many to many relationship between MMEs/S-GWs and eNBs.
While not a limiting environment for these teachings, of particular interest herein is the 3GPP LTE Release 9 (and beyond towards future International Mobile Telecommunications IMT-A systems, such as for example LTE Release 10), referred to herein for convenience simply as Rel-9, or as LTE-Advanced (LTE-A, sometimes termed 4.0G). The current LTE system is Release 8 or Rel-8. Of additional interest herein are deployment scenarios using TDD or FDD mode in a scalable bandwidth manner (of up to, for example, 100 MHz) with a component carrier (CC) aggregation technique. This is shown at FIG. 2, in which there are five adjacent carriers of 20 MHz each to span a LTE-A bandwidth of 100 MHz. FIG. 2 shows some carriers (4 and 5) are compatible with Rel. 8 and therefore accessible by Rel-8 terminals/UEs, while other carriers (1 through 3) are Rel-9 carriers and incompatible with terminals/UEs which operate only under Rel-8 but not Rel-9. Other deployments may find all five carriers Rel-8 compatible, and Release 10 may have a different arrangement of component carrier compatibility. Whether 20 MHz wide or otherwise, each of these adjacent carriers are termed component carriers (CC).
It has been decided that LTE Rel-8 UEs should be able to operate in the LTE-A system. In evolving towards Rel-9, maintaining backwards compatibility with Rel-8 (E-UTRAN) is an important issue. For example, a Rel-8 UE should be able to access a corresponding Rel-9 system, and a Rel-9 UE should be able to access corresponding Rel-8 system, as shown by the arrangement of FIG. 2. Provided that a Rel-8 UE is capable of operating in a scalable system bandwidth of up to 20 MHz (e.g., 10 MHz TDD or 20 MHz TDD) as specified in 3GPP, and that this bandwidth is then scaled up to 100 MHz for Rel-9, the Rel-9 radio system may possibly be structured as a scalable multi-carrier system having at least one Rel-8-compatible carrier.
As can be appreciated, a number of problems can arise in attempting to maintain compatibility between Rel-8 and Rel-9 systems, such as in the uplink control channel design and optimization of that control channel. One requirement of the LTE-A fourth generation (4G) communication network as specified by the International Telecommunications Union (ITU) is the capability for single user multiple-input/multiple-output (SU-MIMO) transmissions, with up to four transmission antennas supported by the LTE-Advanced uplink system.
In Rel-8, the UE transmits control signals to the eNB on a physical uplink control channel (PUCCH). These control signals include ACK/NAK, channel quality indicators (CQI), and scheduling request (SR) indicators. The PUCCH concept of Rel-8 is being extended to LTE-A. To adapt the PUCCH for LTE-A, certain contributors to the 3GPP discussions have suggested that single-carrier transmission should be the target (or at least one option) whenever possible. This is a challenge especially from ACK/NAK signaling point of view because of the CC-specific HARQ and transport block; there will be multiple ACK/NAK bits per UL subframe.
For example, in document R1-090724 (3GPP TSG RAN WG1 Meeting #56, Athens, Greece; 09-13 Feb. 2009; by Nokia Siemens Networks and Nokia, attached to the priority document as Exhibit A), single-carrier properties are maintained by applying Rel-8 TDD principles when signaling multiple ACK/NAK bits per UL subframe. In LTE Rel-8 TDD, in the case of asymmetric DL/UL configuration, the UE has the possibility to report ACK/NAK associated with multiple DL subframes during one UL subframe. The ACK/NAK signaling for multiple DL subframes can be made using either ACK/NAK bundling or an ACK/NAK multiplexing mode.                For the ACK/NAK bundling mode, an AND operation is first performed on the ACK/NAK bits in the time domain to get one bundled ACK/NAK bit (or 2 bits with multi code-word MCW DL transmission), then the bundled bit is modulated and transmitted on the PUCCH channel corresponding to the last detected DL grant.        For the ACK/NAK multiplexing mode, channel selection is used which enables transmission of 2-4 bits via a single PUCCH channel selected from up to 4 PUCCH channels. The selected channel and the used QPSK constellation point are determined based on the ACK/NAK/DTX states for the multiple DL subframes as shown in Table 10.1-2, 10.1-3, and 10.1-4 of 3GPP TS36.213 v850 (attached to the priority document as Exhibit B).        
However, as mentioned above it can only support up to 4 ACK/NAK bits via channel selection among 4 existing PUCCH channels. In the case when the Rel-8 TDD solution is applied with two PUCCH Format 1b resources, it can support up to 3 ACK/NAK bits per subframe via channel selection.
Another proposal is at PCT/EP2009/053214, which relates to Improved ACK/NAK Transmission Method in LTE-Advanced, and which can support up to 6 ACK/NAK bits while at the same time avoid the coverage problem. However, this is achieved by using multiple transmission antennas and so is not useful for UEs having only one transmit antenna as many of the Rel-8 UEs would, and likely some early Rel-9 UEs also.
Also relevant to these teachings is US Patent Publication 2008/0310547 A1 (published Dec. 12, 2008) and entitled “Multi-Code Precoding for Sequence Modulation”. In at least some embodiments, the multi-code precoding detailed there imposes certain requirements for the occupied PUCCH channels, i.e., that they should have the same or adjacent cyclic shift, in order to achieve the cubic metric benefit. These requirements are similar to those in document R1-082589 ((3GPP TSG RAN WG1 Meeting #53bis, Warsaw, Poland; Jun. 30-Jul. 4, 2008; by Nokia and Nokia Siemens Networks, attached to the priority document as Exhibit C).
As further background of the PUCCH in Rel-8, there are currently defined seven SC-FDMA symbols (sometimes termed long blocks or LBs) per slot in the PUCCH structure. A sub-frame consists of two slots. One PUCCH channel occupies two consecutive slots (i.e., one sub-frame) with frequency hopping. Part of those LBs are used for reference signals (the RS part, computer searched zero-autocorrelation codes ZAC sequences in Rel-8) for coherent demodulation. The remaining LBs are used for control and/or data transmission (the data part). In LTE Rel-8, one physical resource block PRB consists of 12 subcarriers during seven symbols, and one PRB contains a data part plus a RS part. Two types of code division multiplexing are used on the PUCCH Format 1/1a/b channel both for the data part and the pilot part: cyclic shifts and cover codes. Cyclic shift multiplexing provides nearly complete orthogonality between different cyclic shifts (if the length of cyclic shift is larger than the delay spread of the radio channel). Rel-8 provides up to 12 orthogonal cyclic shifts within one LB. Orthogonal cover codes (e.g., Walsh or discrete Fourier transform DFT spreading) may be used separately for those LBs corresponding to the RS part and those LBs corresponding to the data part. The CQI (PUCCH Format 2/2a/2b) is typically transmitted in Rel-8 without orthogonal covering.
What is needed in the art is an improved way to signal uplink control signals such as ACK/NAK for the case where the UE occupies multiple UL control channel resources (e.g., 2 or more resources) per subframe.